Composite implant

ABSTRACT

A composite interbody vertebral implant for facilitating fusion of adjacent vertebrae. The implant includes a first endplate of a porous metal material and a second endplate of a porous metal material which are configured to allow bone in-growth. The implant also includes a polymeric body positioned between and bonded to the first and second endplates such that polymeric material of the polymeric body is impregnated into pores of the first and second endplates to bond the components together. The implant may include a cavity extending through the composite implant configured to receive bone growth material to facilitate fusion between a first vertebra and a second vertebra.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/871,295, filed Apr. 26, 2013 which is a continuation of U.S. patentapplication Ser. No. 13/719,295, filed Dec. 19, 2012, now U.S. Pat. No.8,470,042 which is a continuation of U.S. patent application Ser. No.12/829,979, filed Jul. 2, 2010, now U.S. Pat. No. 8,361,150, whichclaims priority to U.S. Provisional Application No. 61/245,115, filed onSep. 23, 2009, the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

The disclosure is directed to composite implants for insertion betweenadjacent vertebrae. More particularly, the disclosure is directed tocomposite interbody vertebral implants formed of joined layers of porousmetal bodies and one or more polymeric bodies, and methods of formingthe same.

BACKGROUND

Chronic back problems cause pain and disability for a large segment ofthe population. Frequently, the cause of back pain is traceable todiseased or degenerated disc material between adjacent vertebrae. Whenthe disc material is diseased, the adjacent vertebrae may beinadequately supported, resulting in persistent pain. Surgicaltechniques have been developed to remove all or part of the diseaseddisc material and fuse the joint between adjacent vertebral bodies.Stabilization and/or arthrodesis of the intervertebral joint can reducethe pain associated with movement of a diseased intervertebral joint.Spinal fusion may be indicated to provide stabilization of the spinalcolumn for a wide variety of spine disorders including, for example,structural deformity, traumatic instability, degenerative instability,post-resection iatrogenic instability, etc.

Generally, fusion techniques involve partial or complete removal of thediseased disc and implanting a vertebral implant or spacer between theadjacent vertebral bodies to facilitate new bone growth between thevertebrae. The surface area, configuration, orientation, surface textureand deformity characteristics of an interbody spacer or bone graftplaced in the disc space can affect the stability of the joint duringfusion and thus affect the overall success of a fusion procedure.

Interbody spacers formed of stainless steel, titanium or titaniumalloys, porous tantalum, and other biocompatible metal alloys are known.Furthermore, interbody spacers formed of polymeric materials such aspolyether ether ketone (PEEK) are also known. With interbody implantsmade out of metal, the metal prevents adequate radiographicvisualization of bone growth through the implant between the vertebrae.Dissimilarly, interbody implants made of a radiolucent material, such aspolyetheretherketone (PEEK), may allow post-operative visualization ofbone growth or fusion through the implant with an imaging device, suchas on an X-ray.

In accordance with the present disclosure, composite implants aredisclosed that can be inserted at a fusion site which may provide anosteoconductive scaffold for bony ingrowth while allowing post-operativevisualization of bone growth or fusion through the implant usingradiographic visualization instrumentation. Methods of manufacturing thecomposite implants are also disclosed.

SUMMARY

The disclosure is directed to several alternative designs, materials andmethods of manufacturing composite interbody implants.

Accordingly, one illustrative embodiment is a composite interbodyvertebral implant for facilitating fusion of adjacent vertebrae. Thecomposite interbody vertebral implant includes a first body of porousmetal, a second body of porous metal, and a polymeric body of athermoplastic polymeric material positioned between the first body ofporous metal and the second body of porous metal. The first body ofporous metal defines a plurality of pores formed by a metallic scaffoldconfigured to allow bone in-growth from a first vertebra. The secondbody of porous metal defines a plurality of pores formed by a metallicscaffold configured to allow bone in-growth from a second vertebra. Afirst interface layer located between the first body of porous metal andthe polymeric body includes the polymeric material impregnated into thepores of the first body of porous metal. A second interface layerlocated between the second body of porous material and the polymericbody includes the polymeric material impregnated into the pores of thesecond body of porous metal. A cavity configured to receive bone growthmaterial to facilitate fusion between the first vertebra and the secondvertebra extends through the composite interbody vertebral implant.

Another illustrative embodiment is a composite interbody vertebralimplant for facilitating fusion of adjacent vertebrae. The compositeinterbody vertebral implant includes a first body of a porous tantalummetal, a second body of a porous tantalum metal, and a polymeric body ofpolyether ether ketone (PEEK) positioned between the first body ofporous tantalum metal and the second body of porous tantalum metal. Thefirst body of porous tantalum metal defines a plurality of pores formedby a metallic scaffold configured to allow bone in-growth from a firstvertebra. The second body of porous tantalum metal defines a pluralityof pores formed by a metallic scaffold configured to allow bonein-growth from a second vertebra. A first interface layer between thefirst body of porous tantalum metal and the polymeric body includespolyether ether ketone (PEEK) of the polymeric body impregnated into thepores of the first body of porous tantalum metal. A second interfacelayer between the second body of porous tantalum metal and the polymericbody includes polyether ether ketone (PEEK) of the polymeric bodyimpregnated into the pores of the second body of porous tantalum metal.

Yet another illustrative embodiment is a method of forming a compositeinterbody vertebral implant. The method includes positioning a firstsurface of a polymeric body of a polymeric material adjacent a surfaceof a first body of a porous metal material. The first body of porousmetal material is heated to a first elevated temperature and acompressive force is applied between the polymeric body of polymericmaterial and the first body of porous metal material, causing a portionof the polymeric material to penetrate into pores of the first body ofporous metal material. A second surface of the polymeric body ofpolymeric material is positioned adjacent a surface of a second body ofa porous metal material. The second body of porous metal material isheated to a second elevated temperature and a compressive force isapplied between the polymeric body of polymeric material and the secondbody of porous metal material, causing a portion of the polymericmaterial to penetrate into pores of the second body of porous metalmaterial.

The above summary of some example embodiments is not intended todescribe each disclosed embodiment or every implementation of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments in connection withthe accompanying drawings, in which:

FIG. 1 is a perspective schematic representation of an exemplarycomposite implant for placement between adjacent vertebrae;

FIG. 2 is an enlarged schematic representation of a portion of theimplant of FIG. 1 showing an interface layer bonding two adjacentmaterials of the composite implant;

FIGS. 3A through 3E illustrate an exemplary method of forming thecomposite implant of FIG. 1;

FIG. 4 is an alternative embodiment of a composite implant for placementbetween adjacent vertebrae;

FIG. 4A is a cross-sectional view of the composite implant of FIG. 4taken along line 4A-4A of FIG. 4;

FIG. 5 is an another alternative embodiment of a composite implant forplacement between adjacent vertebrae;

FIG. 5A is a cross-sectional view of the composite implant of FIG. 5taken along line 5A-5A of FIG. 5;

FIG. 6 is yet another alternative embodiment of a composite implant forplacement between adjacent vertebrae;

FIG. 6A is a cross-sectional view of the composite implant of FIG. 6taken along line 6A-6A of FIG. 6;

FIG. 7 is an image of a composite implant for use in a spinal fusion;

FIG. 8 is an image of an enlarged portion of the composite implant ofFIG. 7 showing the interface layer between a porous metal body and apolymeric body of the composite implant; and

FIGS. 9A and 9B are exploded views of an exemplary fixture forming acomposite implant.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit aspects of the invention tothe particular embodiments described. On the contrary, the intention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about”, whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the term “about” may be indicative asincluding numbers that are rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4,and 5).

Although some suitable dimensions, ranges and/or values pertaining tovarious components, features and/or specifications are disclosed, one ofskill in the art, incited by the present disclosure, would understanddesired dimensions, ranges and/or values may deviate from thoseexpressly disclosed.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The detailed description and the drawings, which are notnecessarily to scale, depict illustrative embodiments and are notintended to limit the scope of the invention. The illustrativeembodiments depicted are intended only as exemplary. Selected featuresof any illustrative embodiment may be incorporated into an additionalembodiment unless clearly stated to the contrary.

Referring now to FIG. 1, there is shown a composite interbody vertebralimplant 10 formed of alternating layers of different materials. Forinstance, the implant may be formed of alternating radioopaque andradiolucent layers, such as metallic layers and polymeric layers bondedtogether at interfaces between the adjacent layers. In some instances,the metallic layers may be formed of a porous metal defining a pluralityof pores formed by a metallic scaffold. As shown in FIG. 1, the implant10 may include a first body 12 of a porous metal material defining aplurality of pores formed by a metallic scaffold and a second body 14 ofa porous metal material defining a plurality of pores formed by ametallic scaffold. For instance, the porous metal material may betantalum, titanium, zirconium, cobalt, chrome and stainless steel, oralloys thereof. In some instances, the pores of the porous metal willhave a pore size of about 150 microns to about 500 microns, or more.However, in other instances a smaller pore size may be desired, such asa pore size of less than about 150 microns. The open cell structure ofthe porous metal scaffold of the first and second bodies 12, 14 ofporous metal may mimic the microstructure of a natural cancellous bone,acting as an osteoconductive matrix for the incorporation of bone,providing optimal permeability and high surface area to encourage newbone in-growth into the pores of the porous metal scaffold of the firstand second bodies 12, 14. Furthermore, the porous metal material mayhave an elastic modulus similar to natural cancellous bone. Forinstance, depending on its porosity, the porous metal may have anelastic modulus of about 1.5 GPa to about 4 GPa, or about 3 GPa, whereasnatural cancellous bone, depending on physiological factors of aspecific patient, may have an elastic modulus of about 0.1 GPa to about3 GPa, or about 0.5 GPa in many instances. In instances in which thefirst body 12 of porous metal is a superior end plate of the implant 10defining a superior surface 18 for engagement with an endplate of thevertebral body of a superior vertebra and/or the second body 14 ofporous metal is an inferior end plate of the implant 10 defining aninferior surface 20 for engagement with an endplate of the vertebralbody of an inferior vertebra, as shown in FIG. 1, the porous metal mayprovide a roughened surface with a high coefficient of friction againstthe vertebral bodies of adjacent vertebrae to resist migration of theimplant 10 once implanted between the vertebrae.

One exemplary porous metal is Trabecular Metal™ material, which is aporous tantalum material marketed by Zimmer Spine, Inc. of Minneapolis,Minn. This material is also disclosed in several U.S. patents,including, for example, U.S. Pat. Nos. 5,282,861, 5,443,515, and6,063,442, the disclosures of which are incorporated herein byreference. These patents describe the formation of a tantalum porousstructure by chemical vapor deposition of tantalum onto a foam carbonstructure.

The implant 10 may also include a polymeric body 16 of a polymericmaterial, such as a thermoplastic polymeric material, positioned betweenthe first and second bodies 12, 14 of porous metal. Some examples ofsuitable thermoplastic polymeric materials include polyether etherketone (PEEK), ultra-high molecular weight polyethylene (UHMWPE),poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), andmixtures or blends thereof. Other suitable polymeric materials includethermoplastic elastomers such as polyurethanes and mixtures or blendsthereof. Such polymeric materials are radiolucent. In some instances thepolymeric material may be chosen such that the polymeric body 16 has anelastic modulus similar to that of natural cancellous bone. Forinstance, polyether ether ketone (PEEK), which has an elastic modulus ofabout 3.6 GPa to about 4.1 GPa, or about 4 GPa, may be chosen such thatthe polymeric body 16 has an elastic modulus similar to that of naturalcancellous bone. The polymer material of the polymeric body 16, such aspolyether ether ketone (PEEK), may also be chosen based on thesimilarity of its elastic modulus to the elastic modulus of the porousmetal used for the first and second bodies 12, 14. For instance, theelastic modulus of the polymeric body 16 may be within about 3.0 GPa orless, about 2.5 GPa or less, about 2.0 GPa or less, or about 1.0 GPa orless of the elastic modulus of the porous metal scaffold of the firstand second bodies 12, 14.

As shown in FIG. 1, and further depicted in FIG. 2, during formation ofthe implant 10, a first interface layer 22 may be formed at theinterface between the first body 12 of porous metal and the polymericbody 16 and a second interface layer 24 may be formed at the interfacebetween the second body 14 of porous metal and the polymeric body 16.The first interface layer 22 may include polymeric material of thepolymeric body 16 impregnated into the pores of the first body 12 ofporous metal. For instance, polymeric material of the polymeric body 16may infuse or penetrate about 1.0 millimeters or more, about 1.2millimeters or more, or about 1.5 millimeters or more into the firstbody 12 of porous metal from the surface of the first body 12 adjacentthe polymeric body 16. In other words, the thickness T₄ of the firstinterface layer 22 including both porous metal and polymeric materialmay be between about 1.0 millimeters to about 2.0 millimeters, about 1.0millimeters to about 1.5 millimeters, about 1.0 millimeters to about 1.2millimeters, about 1.0 millimeters, about 1.1 millimeters, about 1.2millimeters, about 1.3 millimeters, about 1.4 millimeters, or about 1.5millimeters in some instances.

Similarly, the second interface layer 24 may include polymeric materialof the polymeric body 16 impregnated into the pores of the second body14 of porous metal. For instance, polymeric material of the polymericbody 16 may infuse or penetrate about 1.0 millimeters or more, about 1.2millimeters or more, or about 1.5 millimeters or more into the secondbody 14 of porous metal from the surface of the second body 14 adjacentthe polymeric body 16. In other words, the thickness T₅ of the secondinterface layer 24 including both porous metal and polymeric materialmay be between about 1.0 millimeters to about 2.0 millimeters, about 1.0millimeters to about 1.5 millimeters, about 1.0 millimeters to about 1.2millimeters, about 1.0 millimeters, about 1.1 millimeters, about 1.2millimeters, about 1.3 millimeters, about 1.4 millimeters, or about 1.5millimeters in some instances.

As shown in FIG. 2, polymeric material of the polymeric body 16 maypenetrate into and fill pores of the porous metal scaffold of the firstand second bodies 12, 14. Infusing polymeric material into the pores ofthe porous metal scaffold bonds the polymeric body 16 to the first andsecond bodies 12, 14, joining the components together with a mechanicalbond.

The implant 10 may have any desired height H. For instance, the height Hof the implant 10 for use in cervical applications may be about 6millimeters to about 10 millimeters, about 6 millimeters, about 7millimeters, about 8 millimeters, about 9 millimeters, or about 10millimeters. If used in other applications, such as thoracic or lumbarapplications, the implant 10 may have another desired height H.

The thickness T₁ of the first body 12 of porous metal may be about 2millimeters or more, about 2.5 millimeters or more, or about 3millimeters or more in some instances. Thus, after formation, about 1.0millimeters or more, about 1.1 millimeters or more, or about 1.2millimeters or more of the thickness T₁ of the first body 12 may retainopen pores for bone in-growth, while the pores of the remainder of thethickness T₁ may be filled with polymeric material from the polymericbody 16.

Similarly, the thickness T₂ of the second body 14 of porous metal may beabout 2 millimeters or more, about 2.5 millimeters or more, or about 3millimeters or more in some instances. Thus, after formation, about 1.0millimeters or more, about 1.1 millimeters or more, or about 1.2millimeters or more of the thickness T₂ of the second body 14 may retainopen pores for bone in-growth, while the pores of the remainder of thethickness T₂ may be filled with polymeric material from the polymericbody 16.

The polymeric body 16 may have a thickness T₃ after formation of theimplant 10 measured from the lower surface of the first body 12 ofporous metal to the upper surface of the second body 14 of porous metal.For instance the thickness T₃ of the polymeric body 16 of the implant 10for use in cervical applications may be about 2 millimeters to about 8millimeters, about 2 millimeters, about 3 millimeters, about 4millimeters, about 5 millimeters, about 6 millimeters, about 7millimeters, or about 8 millimeters. If used in other applications, suchas thoracic or lumbar applications, the thickness T₃ of the polymericbody 16 of the implant 10 may vary from these dimensions.

It is noted that although the implant 10 is shown as including first andsecond bodies 12, 14, of porous metal defining the superior and inferiorlayers or end plates of the implant 10 joined together by the polymericbody 16 positioned between the first and second bodies 12, 14 of porousmetal, in other embodiments the implant 10 may include additional layersand/or components, and/or alternative orientations of layers and/orcomponents. For instance, the implant 10 could include three or morebodies of porous metal alternating with two or more bodies of polymericmaterial in a horizontal or vertical orientation if desired.

The implant 10 may also include a cavity 26 extending into or throughthe implant 10. As shown in FIG. 1, the cavity 26 may extend through theimplant 10 from the superior surface 18 to the inferior surface 20 ofthe implant 10. In other instances, the cavity 26 may be oriented in adifferent direction, if desired. The cavity 26 may be configured to befilled with bone growth material prior to implanting the implant 10between adjacent vertebrae. The bone growth material may facilitate bonegrowth and fusion between the adjacent vertebrae. In some embodiments, aplurality of cavities 26 may be present to receive bone growth material.The polymeric body 16 may allow post-operative visualization of bonegrowth or fusion through the implant using radiographic visualizationinstrumentation.

FIGS. 3A through 3E illustrate an exemplary method of forming theimplant 10. As shown in FIG. 3A, to form the implant 10, a first body 12of a porous metal may be placed adjacent to a polymeric body 16 of apolymeric material such that a surface of the first body 12 is adjacenta first surface of the polymeric body 16. Furthermore, a second body 14of a porous metal may be placed adjacent the polymeric body 16 such thata surface of the second body 14 is adjacent a second surface of thepolymeric body 16 opposite the first surface. As shown in FIG. 3A, thefirst body 12, the second body 14, and the polymeric body 16 may becylindrically shaped discs in some instances. However, in otherinstances, the first body 12, the second body 14 and the polymeric body16 may be of a different shape, if desired.

The pre-bonded assembly 10′, or components thereof, may be placed into amold 50. The mold 50 may be sized such that the periphery of thepre-bonded assembly 10′ closely approximates the periphery of theinterior of the mold 50. For instance, the interior of the mold 50 mayhave a diameter sized slightly larger than the diameter of thecomponents of the pre-bonded assembly 10′.

With the pre-bonded assembly 10′, or components thereof, positioned inthe mold 50, the first body 12 of porous metal and/or the second body 14of porous metal may be heated by a heat source H to an elevatedtemperature, shown at FIG. 3B. For example, the first body 12 of porousmetal and/or the second body 14 of porous metal may be heated to anelevated temperature in the range of about 60° C. to about 450° C., inthe range of about 80° C. to about 400° C., about 140° C. to about 360°C., about 300° C. to about 400° C., about 340° C. to about 400° C., orabout 350° C. to about 400° C., in some instances. It is desirable thatthe elevated temperature be greater than or equal to the glasstransition temperature of the polymeric material of the polymeric body16. In some instances, the elevated temperature may be less than orequal to the melting temperature of the polymeric material of thepolymeric body 16. In other instances, the elevated temperature may begreater than or equal to the melting temperature of the polymericmaterial of the polymeric body 16. The glass transition temperature (Tg)and the melting temperature (Tm) of some suitable polymeric materialsare listed in Table 1, below.

TABLE 1 Glass Transition and Melting Temperatures of Some SuitablePolymeric Materials Material UHMWPE PMMA PEEK PET Tg (° C.) ~−160 ~105~143 ~65 Tm (° C.) ~135 — ~340 ~260

The first body 12 and/or second body 14 may be heated through inductionheating. For instance, infrared, radiofrequency, laser or ultra-soundenergy from the heating source H may be used to heat the first body 12of porous metal and/or the second body 14 of porous metal to an elevatedtemperature in the mold 50. In other instances, the first body 12, thesecond body 14 and/or the polymeric body 16 may be heated throughconduction heating. While other techniques are contemplated, somesuitable techniques for bonding the polymeric body 16 to the first body12 and/or the second body 14 include, but are not limited to, ultrasonicwelding, linear vibration welding, orbital vibration welding, spinwelding, hot plate welding, laser IRAM welding, etc.

As shown in FIG. 3C, concurrently with and/or subsequent to heating thefirst body 12 and/or the second body 14, a compressive force F may beapplied to the first body 12 and/or the second body 14 to compress thefirst body 12 against the first surface of the polymeric body 16 and/orto compress the second body 14 against the second surface of thepolymeric body 16 in the mold 50. Such a process may be described as ahot-stamping process in which the first body 12 and/or the second body14 is pressed against the polymeric body 16 while the first body 12and/or the second body 14 is at an elevated temperature.

As the first body 12 is pressed against the first surface of thepolymeric body 16 in the mold 50, the first surface of the polymericbody 16 is heated through conduction heating from the first body 12,softening the polymeric material of the polymeric body 16 proximate thefirst surface of the polymeric body 16. The compressive force F forcespolymeric material at the first surface of the polymeric body 16 intothe pores of the porous scaffold of the first body 12, infusingpolymeric material into a portion of the first body 12 proximate thepolymeric body 16. In some instances, the compressive force F may bebetween about 1 pound to about 100 pounds of force, between about 1pound to about 20 pounds of force, about 1 pound to about 5 pounds offorce, or about 1 pound to about 2 pounds of force. The force F may bemaintained for any desired duration of time. For example, the force Fmay be maintained for 15 seconds or more, 30 seconds or more, 1 minuteor more, or 5 minutes or more in some instances. Pressure applied at theinterface between the first body 12 and the polymeric body 16 may bebetween about 1.25 lb/in² to about 125 lb/in², or about 1.25 lb/in² toabout 12.5 lb/in², or about 1.25 lb/in² to about 2.5 lb/in², in someinstances. In some instances, the pressure applied may be between 0 psito about 1000 psi. For instance, the pressure may be about 400 psi ormore, about 500 psi or more, about 600 psi or more, about 700 psi ormore, about 800 psi or more, or about 900 psi or more.

Similarly, as the second body 14 is pressed against the second surfaceof the polymeric body 16 in the mold 50, the second surface of thepolymeric body 16 is heated through conduction heating from the secondbody 14, softening the polymeric material of the polymeric body 16proximate the second surface of the polymeric body 16. The compressiveforce F forces polymeric material at the second surface of the polymericbody 16 into the pores of the porous scaffold of the second body 14,infusing polymeric material into a portion of the second body 14proximate the polymeric body 16. In some instances, the compressiveforce F may be between about 1 pound to about 100 pounds of force,between about 1 pound to about 20 pounds of force, about 1 pound toabout 5 pounds of force, or about 1 pound to about 2 pounds of force.The force F may be maintained for any desired duration of time. Forexample, the force F may be maintained for 15 seconds or more, 30seconds or more, 1 minute or more, or 5 minutes or more in someinstances. Pressure applied at the interface between the second body 14and the polymeric body 16 may be between about 1.25 lb/in² to about 125lb/in², or about 1.25 lb/in² to about 12.5 lb/in², or about 1.25 lb/in²to about 2.5 lb/in², in some instances. In some instances, the pressureapplied may be between 0 psi to about 1000 psi. For instance, thepressure may be about 400 psi or more, about 500 psi or more, about 600psi or more, about 700 psi or more, about 800 psi or more, or about 900psi or more.

Throughout the bonding process, a portion of the polymeric body 16 maybe maintained at a temperature below the glass transition temperature ofthe polymeric material of the polymeric body 16, while the first andsecond surfaces of the polymeric body 16 adjacent the first and secondbodies 12, 14, respectively, are heated to an elevated temperaturethrough conduction heating from the first and second bodies 12, 14. Forinstance, during the bonding process, the first and second surfaces ofthe polymeric body 16 may be heated to a temperature greater than orequal to the glass transition temperature of the polymeric material ofthe polymeric body 16 while a central portion of polymeric body 16 ismaintained at a temperature below the glass transition temperature ofthe polymeric material.

Resultant of the bonding process, a bonded assembly 10″ of the firstbody 12, the second body 14 and the polymeric body 16 joined togethermay be formed. The bonded assembly 10″ may then be removed from the mold50, as shown in FIG. 3D. Subsequently, the bonded assembly 10″ may beshaped into any desired shape such as the shape of the implant 10 shownin FIG. 3E. Various techniques known in the art may be used to shape thebonded assembly 10″ into the final implant 10.

Although it has been illustrated to simultaneously bond the first andsecond bodies 12, 14 to the polymeric body 16, in some embodiments, thefirst body 12 may be heated to an elevated temperature and compressedagainst the first surface of the polymeric body 16 in the mold 50 at onestage of the forming process and the second body 14 may be heated to anelevated temperature and compressed against the second surface of thepolymeric body 16 in the mold 50 at a later stage of the formingprocess.

The implant 10 may be used in a spinal fusion procedure to fuse adjacentvertebrae in order to provide stabilization of the spinal column of apatient suffering from a spinal disorder. For example, after accessingthe spinal column of the patient in a percutaneous technique, aminimally invasive technique, an open technique or other technique, adiscectomy may be performed to remove at least a portion of a damaged ordegenerated intervertebral disc (i.e., spinal disc) between adjacentvertebrae to create a space to insert the implant 10 between thesuperior vertebra and the inferior vertebra. In one exemplary procedure,a small window is cut in the annulus of the intervertebral disc andportions of the nucleus pulposus is removed through the window to createthe space. Once the space has been created, the implant 10 may beinserted into the disc space between the superior vertebra and theinferior vertebra such that the superior surface 18 of the implant 10contacts the end plate of the vertebral body of the superior vertebraand the inferior surface 20 of the implant 10 contacts the end plate ofthe vertebral body of the inferior vertebra. Thus, a surface of thefirst body 12 of porous metal may contact the superior vertebra and asurface of the second body 14 of porous metal may contact the inferiorvertebra. The high coefficient of friction between the first body 12 andthe end plate of the superior vertebra and the high coefficient offriction between the second body 14 and the end plate of the inferiorvertebra due to the roughness of the porous metal may facilitatemigration of the implant once installed between the vertebrae. The firstand second bodies 12, 14 of porous metal may also allow bone in-growthinto the pores of the porous metal from the end plates of the superiorand inferior vertebrae, respectively and promote fusion of the adjacentvertebrae.

The first body 12 of porous metal, the second body 14 of porous metal,and the polymeric body 26 may be configured to bear the axial loadingfrom the end plates of the adjacent vertebrae. With the implant 10, theentire axial load between the adjacent vertebra is transferred from theend plate of the superior vertebra to the first body 12 of porous metal,from the first body 12 of porous metal to the polymeric body 16, fromthe polymeric body 16 to the second body 14 of porous metal, and fromthe second body 14 of porous metal to the end plate of the inferiorvertebra. Thus, the entire axial load between the adjacent vertebrae maybe transferred through each of the first body 12 of porous metal, thepolymeric body 16, and the second body 14 of porous metal. Thus, theimplant 10 may provide load bearing support as well as the properspacing between the adjacent vertebrae while fusion of the vertebraetakes place.

Prior to being inserted into the disc space created by the removal ofintervertebral disc material, the cavity 26 of the implant 10 may bepacked or filled with bone growth material to facilitate fusion betweenthe superior and inferior vertebrae in order to immobilize the adjacentvertebrae. Bone growth material may include bone growth inducingmaterial, bone grafting material, or any other type of material thatpromotes or encourages bone growth or bone fusion.

The presence of the polymeric body 16, formed of a radiolucent material,which at least in part defines the cavity 26, allows medical personnelthe ability to assess fusion between the adjacent vertebrae through thefusion implant 10 using a radiographic technique during a post-operativeprocedure. Thus, the progression and status of the fusion can bemonitored and checked post-operatively through the use of a radiographictechnique (e.g., x-ray) without the metallic components of the implant10 obstructing visualization of fusion between the adjacent vertebrae.

Thus, the presence of the first and second bodies 12, 14 of porous metalprovide the implant 10 with an osteoconductive scaffold mimicking thetrabecular architecture of natural cancellous bone which promotes bonein-growth and migration resistance, while the radiolucency of thepolymeric body 16 allows for post-operative visualization through theimplant 10 with a radiographic visualization technique to monitorprogression and status of fusion between the adjacent vertebrae.Additionally, the materials of each of the first body 12 of porousmetal, the second body 14 of porous metal, and the polymeric body 16 maybe chosen such that they each have a modulus of elasticity approximatingthe modulus of elasticity of natural cancellous bone to reduce stressshielding at the fusion site.

Another embodiment of a composite implant 110 is shown in FIGS. 4 and4A. The implant 110 may be formed of a first body 112 of a porous metalmaterial defining a plurality of pores formed by a metallic scaffold anda second body 114 of a porous metal material defining a plurality ofpores formed by a metallic scaffold. The implant 110 may also include apolymeric body 116 of a polymeric material, such as a thermoplasticpolymeric material, positioned between the first and second bodies 112,114 of porous metal.

The first body 112 of porous metal may be of an annular shape located ata superior surface of the implant 110 for contact with the end plate ofa superior vertebra in a spinal fusion procedure. The second body 114 ofporous metal may be of an annular shape located at an inferior surfaceof the implant 110 for contact with the end plate of an inferiorvertebra in a spinal fusion procedure.

Although not expressly illustrated in the figures, the interface betweenthe first body 112 and the polymeric body 116 may include polymericmaterial of the polymeric body 116 impregnated into the pores of thefirst body 112 of porous metal similar to that described above regardingthe implant 10. Furthermore, the interface between the second body 114and the polymeric body 116 may include polymeric material of thepolymeric body 116 impregnated into the pores of the second body 114 ofporous material similar to that described above regarding the implant10.

The implant 110 may also include a cavity 126 extending into or throughthe implant 110. As shown in FIG. 4, the cavity 126 may extend throughthe implant 110 from the superior surface to the inferior surface of theimplant 110. In other instances, the cavity 126 may be oriented in adifferent direction, if desired. The cavity 126 may be configured to befilled with bone growth material prior to implanting the implant 110between adjacent vertebrae. The bone growth material may facilitate bonegrowth and fusion between the adjacent vertebrae. In some embodiments, aplurality of cavities 126 may be present to receive bone growthmaterial. The polymeric body 116 may allow post-operative visualizationof bone growth or fusion through the implant using radiographicvisualization instrumentation, while the first and second bodies 112,114 of porous metal may allow bone for in-growth and migrationresistance of the implant 110.

The implant 110 may be formed with a process similar to that describedabove. For example, the implant 110 may be formed by heating the firstand second bodies 112, 114 of porous metal to an elevated temperature,such as by induction heating, and pressing the first and second bodies112, 114 against the polymeric body 116. The surface of the polymericbody 116 against the first and second bodies 112, 114 may be heated andsoftened through conduction heating by the first and second bodies 112,114. Polymeric material may thus be impregnated into pores of the firstand second bodies 112, 114 of porous metal to bond the first and secondbodies 112, 114 to the polymeric body 116, while a portion of thepolymeric body 116 is maintained at a temperature less than the glasstransition temperature of the polymeric material. The implant 110 may beshaped as desired.

Another embodiment of a composite implant 210 is shown in FIGS. 5 and5A. The implant 210 may be formed of a first body 212 of a porous metalmaterial defining a plurality of pores formed by a metallic scaffold anda second body 214 of a porous metal material defining a plurality ofpores formed by a metallic scaffold. The implant 210 may also include apolymeric body 216 of a polymeric material, such as a thermoplasticpolymeric material, positioned between the first and second bodies 212,214 of porous metal.

The first body 212 of porous metal may be of an annular shape located ata superior surface of the implant 210 for contact with the end plate ofa superior vertebra in a spinal fusion procedure. The second body 214 ofporous metal may be of an annular shape located at an inferior surfaceof the implant 210 for contact with the end plate of an inferiorvertebra in a spinal fusion procedure.

Although not expressly illustrated in the figures, the interface betweenthe first body 212 and the polymeric body 216 may include polymericmaterial of the polymeric body 216 impregnated into the pores of thefirst body 212 of porous metal similar to that described above regardingthe implant 10. Furthermore, the interface between the second body 214and the polymeric body 216 may include polymeric material of thepolymeric body 216 impregnated into the pores of the second body 214 ofporous material similar to that described above regarding the implant10.

The implant 210 may also include a cavity 226 extending into or throughthe implant 210. As shown in FIG. 5, the cavity 226 may extend throughthe implant 210 from the superior surface to the inferior surface of theimplant 210. The annular shape of the first and second bodies 212, 214may, in part, define the cavity 226 extending through the implant 210.In other instances, the cavity 226 may be oriented in a differentdirection, if desired. The cavity 226 may be configured to be filledwith bone growth material prior to implanting the implant 210 betweenadjacent vertebrae. The bone growth material may facilitate bone growthand fusion between the adjacent vertebrae. In some embodiments, aplurality of cavities 226 may be present to receive bone growthmaterial. The polymeric body 216 may allow post-operative visualizationof bone growth or fusion through the implant using radiographicvisualization instrumentation, while the first and second bodies 212,214 of porous metal may allow bone for in-growth and migrationresistance of the implant 210.

The implant 210 may be formed with a process similar to that describedabove. For example, the implant 210 may be formed by heating the firstand second bodies 212, 214 of porous metal to an elevated temperature,such as by induction heating, and pressing the first and second bodies212, 214 against the polymeric body 216. The surface of the polymericbody 216 against the first and second bodies 212, 214 may be heated andsoftened through conduction heating by the first and second bodies 212,214. Polymeric material may thus be impregnated into pores of the firstand second bodies 212, 214 of porous metal to bond the first and secondbodies 212, 214 to the polymeric body 216, while a portion of thepolymeric body 216 is maintained at a temperature less than the glasstransition temperature of the polymeric material. The implant 210 may beshaped as desired.

Another embodiment of a composite implant 310 is shown in FIGS. 6 and6A. The implant 310 may be formed of a first body 312 of a porous metalmaterial defining a plurality of pores formed by a metallic scaffold anda second body 314 of a porous metal material defining a plurality ofpores formed by a metallic scaffold. The implant 310 may also include apolymeric body 316 of a polymeric material, such as a thermoplasticpolymeric material, positioned between the first and second bodies 312,314 of porous metal.

The first body 312 of porous metal may extend from the superior surfaceto the inferior surface along a lateral surface of the implant 310,providing contact with the end plates of superior and inferior vertebraein a spinal fusion procedure. The second body 314 of porous metal mayextend from the superior surface to the inferior surface along acontra-lateral surface of the implant 310, providing contact with theend plates of superior and inferior vertebrae in a spinal fusionprocedure.

Although not expressly illustrated in the figures, the interface betweenthe first body 312 and the polymeric body 316 may include polymericmaterial of the polymeric body 316 impregnated into the pores of thefirst body 312 of porous metal similar to that described above regardingthe implant 10. Furthermore, the interface between the second body 314and the polymeric body 316 may include polymeric material of thepolymeric body 316 impregnated into the pores of the second body 314 ofporous material similar to that described above regarding the implant10.

The implant 310 may also include a cavity 326 extending into or throughthe implant 310. As shown in FIG. 6, the cavity 326 may extend throughthe implant 310 from the superior surface to the inferior surface of theimplant 310. In other instances, the cavity 326 may be oriented in adifferent direction, if desired. The cavity 326 may be configured to befilled with bone growth material prior to implanting the implant 310between adjacent vertebrae. The bone growth material may facilitate bonegrowth and fusion between the adjacent vertebrae. In some embodiments, aplurality of cavities 326 may be present to receive bone growthmaterial. The polymeric body 316 may allow post-operative visualizationof bone growth or fusion through the implant using radiographicvisualization instrumentation, while the first and second bodies 312,314 of porous metal may allow bone for in-growth and migrationresistance of the implant 310.

The implant 310 may be formed with a process similar to that describedabove. For example, the implant 310 may be formed by heating the firstand second bodies 312, 314 of porous metal to an elevated temperature,such as by induction heating, and pressing the first and second bodies312, 314 against the polymeric body 316. The surface of the polymericbody 316 against the first and second bodies 312, 314 may be heated andsoftened through conduction heating by the first and second bodies 312,314. Polymeric material may thus be impregnated into pores of the firstand second bodies 312, 314 of porous metal to bond the first and secondbodies 312, 314 to the polymeric body 316, while a portion of thepolymeric body 316 is maintained at a temperature less than the glasstransition temperature of the polymeric material. The implant 310 may beshaped as desired.

An image of a composite implant for use in a spinal fusion is shown inFIG. 7. FIG. 8 is an image of an enlarged portion of the compositeimplant of FIG. 7 showing the interface layer between a porous metalbody and a polymeric body of the composite implant. From FIGS. 7 and 8,it can be seen that polymeric material from the polymeric body 16 isimpregnated into the pores of the porous metal scaffold of the first andsecond bodies 12, 14 to mechanically bond the polymeric body 16 betweenthe first and second bodies 12, 14 of porous metal.

It is also contemplated that an interbody implant which is formedentirely of a porous metal material defining a plurality of pores formedby a metallic scaffold, as described herein, may include one or morewindows or openings extending entirely through the interbody implantwhich may aid in allowing post-operative visualization of bone growth orfusion through the implant with an imaging device, such as on an X-ray.Such an implant may be designed to include one or more windows orientedin a superior-inferior orientation, an anterior-posterior orientation,and/or a medial-lateral orientation for visualization purposes. Thus,post-operative visualization in a direction corresponding to theorientation of the window(s) may allow visualization of bone growththrough the implant without porous metal material from the implantobstructing the image. Care should be taken to ensure the implantretains sufficient structural integrity to withstand the compressiveforces experienced through the spinal column in circumstances in whichan implant formed entirely of a porous metal scaffold including windowsextending therethrough is used.

FIGS. 9A and 9B are exploded views illustrating an exemplary embodimentof a fixture 400 configured for forming a composite implant as describedherein. The fixture 400 includes an upper block 402, a lower block 404,and one or more, or a plurality of side plates 406. The side plate(s)406 may be configured to collectively surround components of a compositeimplant during a molding process. Stated differently, the side plate(s)406 may define a cavity 408 in which the components of the compositeimplant are positioned during a molding process. As shown in FIGS. 9Aand 9B, the fixture 400 may include two side plates 406 whichcollectively define the cavity 408. In other embodiments, however, thefixture 400 could include one, three, four, five, six or more sideplates 406 arranged to collectively define the cavity 408. The cavity408 may be any desired shape, such as circular, rectangular, square,oval, etc. The shape and size of the cavity 408 may closely approximatethe shape and size of the components of the composite implant to bemolded together with the fixture 400. It is noted that varioustechniques known in the art may be used to shape the bonded assembly ofcomponents into the final composite implant subsequent to the moldingprocess, thus the shape of the cavity 408 need not necessarily reflectthe shape of the final composite implant, but may in some instances.

The fixture 400 may also include a compression mechanism 410 configuredto apply a compressive force to the implant components positioned in thecavity 408. The compression mechanism 410 may be positioned, at least inpart, within a bore 412 of the upper block 402. The compressionmechanism 410 may include a spring member, such as a helical spring 414positioned between a pair of spring plungers 416.

The fixture 400 may also include an adjustment mechanism for selectivelyadjusting the amount of pressure exerted onto the components of thecomposite implant during the molding process. For example, the fixture400 may include a threaded screw 418 threadably received in a threadedbore 420 in the upper block 402. The threaded screw 418 may include ahead portion or knob 422 which may be manipulated to rotate the screw418 in the threaded bore 420 to move the screw 418 toward and/or awayfrom the spring 414 in order to adjust the compression of the spring414, and thus adjust the amount of pressure exerted onto the componentsof the composite implant.

The upper block 402 may also include one or more, or a plurality ofopenings 424 extending through the upper block 402 from a perimetersurface of the upper block 402 to the bore 412 in order to visuallyinspect the compression mechanism 410 and/or visually ascertain theamount of compression of the spring 414 and thus the amount of pressureexerted on the composite implant during the molding process.

When assembled, the side plate(s) 406 may be positioned between thelower block 404 and the upper block 402 with the compression mechanism410 positioned in the bore 412 of the upper block 402. So arranged, afirst plunger 416 of the compression mechanism 410 may be positionedbetween the spring 414 and the composite implant positioned in thecavity 408, and a second plunger 416 of the compression mechanism 410may be positioned between the spring 414 and the screw 418. During amolding process, the components of the composite implant may bepositioned in the cavity 408 with the composite implant positionedbetween the lower block 404 and the first plunger 416 of the compressionmechanism 410. The upper block 402, lower block 404 and/or side plate(s)406 may be secured together, for example, with threaded fasteners (notshown) or other fastening means.

During a molding process, compressive forces exerted on the compositeimplant in the cavity 408 may compress the composite implant between thelower plate 404 and the first plunger 416, while the side plate(s) 406surround the sides of the composite implant. Accordingly, the spring414, which is under a desired amount of compression, may push the firstplunger 416 against the upper surface of the composite implant while thelower surface of the composite implant is pressed against the lowerblock 404. The compressive force exerted on the composite implant may beadjusted by rotating the screw 418 in the threaded bore 420 to move thescrew 418 toward and/or away from the spring 414. Moving the screw 418toward the spring 414 shortens or compresses the spring 414, whereasmoving the screw 418 away from the spring 414 lengthens or decompressesthe spring 414. Thus, adjusting the length of the spring 414 with thescrew 418 may adjust the compressive force exerted on the compositeimplant. In some instances, the pressure applied may be between 0 psi toabout 1000 psi. For instance, the pressure may be about 100 psi or more,about 200 psi or more, about 300 psi or more, about 400 psi or more,about 500 psi or more, about 600 psi or more, about 700 psi or more,about 800 psi or more, or about 900 psi or more.

During the molding process, the composite implant may be formed with aprocess similar to that described above. For example, the compositeimplant, the components of which are disposed in the cavity 408, may beformed by heating the first and second bodies of porous metal of thecomposite implant to an elevated temperature, and pressing the first andsecond bodies against the polymeric body positioned therebetween. Thepolymeric body, or at least the surfaces of the polymeric body againstthe first and second bodies of porous metal, may be heated and softened,allowing polymeric material to be impregnated into pores of the firstand second bodies of porous metal to bond the first and second bodies tothe polymeric body by the compressive forces exerted against thecomposite implant. When the polymeric body of the composite implant (orportions thereof) is heated to an elevated temperature, the sideplate(s) 406 contain the flow of the polymeric material, and thusmaintain the shape of the polymeric body. In some instances, a portionof the polymeric body may be maintained at a temperature less than theglass transition temperature of the polymeric material, while portionsof the polymeric body adjacent the first and second bodies of porousmetal may be heated to a temperature greater than or equal to the glasstransition temperature of the polymeric material.

In some instances, the fixture 400, with the components of the compositeimplant (e.g., first and second bodies of porous metal and the polymericbody) positioned in the cavity 408 and a desired compressive forceapplied thereto by the compression mechanism 410, may be placed in anoven (not shown), such as a vacuum oven, configured to heat thecomponents of the composite implant to an elevated temperature duringthe molding process. In some instances, the oven may heat the componentsof the composite implant through conduction, convection, and/orinduction heating.

In some instances, the oven may be purged of air to make the chamber ofthe oven in which the fixture 400 in placed free of oxygen and/ornitrogen. In some instances, the oven may be filled with an inert gas,such as argon or helium. In some instances, the temperature within thechamber of the oven holding the fixture 400 and composite implant may beincreased to an elevated temperature in the range of about 60° C. toabout 450° C., in the range of about 80° C. to about 400° C., about 140°C. to about 360° C., about 300° C. to about 400° C., about 340° C. toabout 400° C., or about 350° C. to about 400° C., in some instances. Itis desirable that the elevated temperature within the oven be greaterthan or equal to the glass transition temperature of the polymericmaterial of the polymeric body of the composite implant. In someinstances, the elevated temperature may be less than or equal to themelting temperature of the polymeric material of the polymeric body ofthe composite implant. In other instances, the elevated temperature maybe greater than or equal to the melting temperature of the polymericmaterial of the polymeric body of the composite implant.

While in the oven at the elevated temperature, the compression mechanism410 of the fixture 400 may apply pressure against the composites of thecomposite implant. For example, in some instances the compressionmechanism 410 may be adjusted to apply a pressure between 0 to about1000 psi. In some instances, the applied pressure may be about 400 psior more, about 500 psi or more, about 600 psi or more, about 700 psi ormore, about 800 psi or more, or about 900 psi or more. For example, theapplied pressure may be in the range of about 500 psi to about 800 psi,in the range of about 600 psi to about 800 psi, or in the range of about700 psi to about 800 psi in some instances.

The elevated temperature softens the polymeric material which thecompressive forces exerted on the porous metal bodies causes polymericmaterial of the polymeric body to be pushed into the pores of the porousmetal bodies, mechanically locking the components together. Subsequentto the molding process, the fixture 400 with the composite implant maybe removed from the oven, the composite implant may be removed from thefixture 400, and the composite implant may be shaped as desired.

Those skilled in the art will recognize that the present invention maybe manifested in a variety of forms other than the specific embodimentsdescribed and contemplated herein. Accordingly, departure in form anddetail may be made without departing from the scope and spirit of thepresent invention as described in the appended claims.

What is claimed is:
 1. A composite vertebral implant for positioningbetween adjacent vertebrae, the composite vertebral implant comprising:a ring-like thermoplastic polymeric body having an inner surface and aninner shelf portion, the inner shelf portion having a first ledgesurface and a second ledge surface; a first ring-like porous memberhaving a plurality of pores formed therein, the first ring-like porousmember having a first surface on a first side of the first ring-likeporous member; a second ring-like porous member having a plurality ofpores formed therein, the second ring-like porous member having a firstsurface on a first side of the second ring-like porous member; whereinthe first surface of the first-ring like porous member is configured tocontact the first ledge surface of the inner shelf portion of thering-like polymeric body; and wherein the first surface of the secondring-like porous member is configured to contact the second ledgesurface of the inner shelf portion of the ring-like polymeric body. 2.The composite vertebral implant of claim 1, wherein the plurality of thepores proximate the first surface of the first ring-like porous memberare mechanically connected to a portion of the thermoplastic materialproximate the first ledge surface of the inner shelf portion of thering-like polymeric body.
 3. The composite vertebral implant of claim 2,wherein the plurality of the pores proximate the first surface of thesecond ring-like porous member are mechanically connected to a portionof the thermoplastic material proximate the second ledge surface of theinner shelf portion of the ring-like polymeric body.
 4. The compositevertebral implant of claim 3, wherein the plurality of pores proximatethe first surface of the second ring-like porous member are filled witha portion of the thermoplastic material proximate the second ledgesurface of the inner shelf portion of the ring-like polymeric body. 5.The composite vertebral implant of claim 2, wherein the plurality of thepores proximate the first surface of the first ring-like porous memberare filled with a portion of the thermoplastic material proximate thefirst ledge surface of the inner shelf portion of the ring-likepolymeric body.
 6. The composite vertebral implant of claim 1, whereinthe first ring-like porous member includes a second surface on a secondside of the first ring-like porous member, and wherein the secondsurface of the first ring-like porous member is configured to bepositioned against a first vertebra.
 7. The composite vertebral implantof claim 6, wherein the second ring-like porous member includes a secondsurface on a second side of the first ring-like porous member, andwherein the second surface of the second ring-like porous member isconfigured to be positioned against a second vertebra.
 8. The compositevertebral implant of claim 7, further including a cavity, wherein thecavity extends from the second surface of the first ring-like porousmember to the second surface of the second ring-like porous member. 9.The composite vertebral implant of claim 8, wherein the cavity ifconfigured to receive bone graft material therein.
 10. The compositevertebral implant of claim 7, wherein the second surface of the firstring-like porous member is configured promote bone in-growth into aportion of the plurality of pores proximate the second surface of thefirst ring-like porous member.
 11. The composite vertebral implant ofclaim 10, wherein the second surface of the second ring-like porousmember is configured promote bone in-growth into a portion of theplurality of pores proximate the second surface of the second ring-likeporous member.
 12. The composite vertebral implant of claim 1, whereinthe ring-like thermoplastic polymeric body surrounds a perimeter of thefirst ring-like porous member and a perimeter of the second ring-likeporous member.
 13. The composite vertebral implant of claim 1, whereinthe first and the second ring-like porous members are formed of a porousmetal material having a modulus of elasticity of about 1.5 to about 4GPa.
 14. The composite vertebral implant of claim 13, wherein thepolymeric body has a modulus of elasticity within about 3.0 GPa of themodulus of the elasticity of the porous metal material.
 15. Thecomposite vertebral implant of claim 1, wherein the first and secondring-like porous members are formed of a porous metal material having amodulus of elasticity of about 3 to 4 GPa and the ring-like polymericbody has a modulus of elasticity within about 1 GPa of the modulus ofelasticity of the porous metal material.
 16. The composite vertebralimplant of claim 1, wherein the first and the second ring-like porousmembers are formed of a porous tantalum.
 17. The composite vertebralimplant of claim 16, wherein the polymeric body is a polyether etherketone (PEEK).
 18. A composite vertebral implant for positioning betweenadjacent vertebrae, the composite vertebral implant comprising: a firstring-like porous member having a plurality of pores formed therein, thefirst ring-like porous member having a first surface on a first side ofthe first ring-like porous member and a second surface on a second sideof the first ring-like porous member; a second ring-like porous memberhaving a plurality of pores formed therein, the second ring-like porousmember having a first surface on a first side of the second ring-likeporous member and a second surface on a second side of the secondring-like porous member; a ring-like thermoplastic polymeric body havingan inner shelf portion, the inner shelf portion having a first ledgesurface and a second ledge surface, and wherein the inner shelf portionis positioned between the first surface of the first ring-like porousmember and the first surface of the second ring-like porous member; anda cavity extending from the second surface of the first ring-like porousmember to the second surface of the second ring-like porous member. 19.The composite vertebral implant of claim 18, wherein a plurality of thepores proximate the first surface of the first ring-like porous memberare filled by a portion of the thermoplastic ring-like polymeric body.20. The composite vertebral implant of claim 19, wherein a plurality ofthe pores proximate the first surface of the second ring-like porousmember are filled by a portion of the thermoplastic ring-like polymericbody.